Using some of the ideas presented by rformato, I've significantly sped up $("#id") selection. It's now just 10% slower than doing: $(document.getElementById("test")), which seems quite acceptable. (Bug #1316)

Fix for a selector speed regression (calling a simple selector many times resulted in a significant speed down). This has been fixed by breaking the RegExps out into the global scope. This required that a closure be implemented around the full jQuery script (which is now the case). Some simple changes were made in addition to the RegExp one, allowing for some greater flexibility on our part - and hopefully better compression.
Speed results:
http://dev.jquery.com/~john/ticket/1351/ vs.
http://dev.jquery.com/~john/ticket/1351/113.html vs.
http://dev.jquery.com/~john/ticket/1351/112.html

Complete overhaul of the Ajax test suite, it's now passing in all browsers. In order to achieve this I had to fix a numbe
r of bugs in the suite itself, along with other random bugs that popped up. The following bugs were resolved along the wa
y: #1236 (.extend() keeps processing when it hits nulls), #1028 (.extend() now works recursively), #1080 ($.get no longer
overwrites the data parameter), #1210 (Creating script and link tags now work), and #1463 (jQuery.global has been re-too
led to no longer leak memory and slow things down).